Foundry technique for the manufacture of heavy wall thickness valves and fittings for nuclear application



May 27, 1969 R. R. WALTIEN 3,446,236

FOUNDRY TECHNIQUE FOR THE MANUFACTUR F' HEAVY WALL THICKNESS VALVES AND FITTIN FOR NUCLEAR APPLICATION Filed Jan. 2e, 196e INVENTOR. ROBE/2T E. WALT/EN United States Patent O FOUNDRY TECHNIQUE FOR THE MANUFAC- TURE OF HEAVY WALL THICKNESS VALVES AND FITTINGS FOR NUCLEAR APPLICATION Robert R. Waltien, 8935 116th St.,

Richmond Hill, N.Y. 11418 Filed Jan. 26, 1966, Ser. No. 523,510 Int. Cl. F161 59/16; F16k 51/00 U.S. Cl. 137-375 1 Claim ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improved foundry techniques for founding castings for exceptionally demanding service and more particularly to founding completely sound fluid system components having wall thickness Well in excess of one inch.

Conventional sand foundry techniques comprises forming a cavity in a sand mold with a pattern which is a replica of the casting desired. Interior surfaces of a hollow casting are defined by a sand core which is located in the mold. The mold is formed Iwith an inlet for the pour metal and one or -more outlets for the air which also serve as reservoirs for the excess pour metal. Suliicient metal is poured into the inlet to lill the cavity around the core plus the inlet and reservoirs. That part of the pour metal which solidifies in the inlet is designated the gate and that part of the pour metal which solidilies in the reservoirs is designated the riser(s). The reservoirs supply molten metal to the casting as it shrinks. `If the casting is thick-walled, shrinkage becomes a serious problem. .It becomes more ditlicult to provide sufficient reservoirs, properly located, to supply the metal required by the casting as it shrinks, `as casting wall thickness is increased.

Modern deeper diving submarines require valves and other fluid system components that are absolutely reliable at the high operating pressures of the submarines. Nuclear reactors require valves and other uid system components that are reliable at combined high operating pressures and high operating temperatures. Advancing technology is expected to add to the need for such high strength cast components. Components for these applications have been made with progressively greater =wall thickness. Valve and fitting castings for more ordinary service may have wall thickness up to about 11/2 inches. Foundry techniques including gating and risering for those castings have wall thickness up to about 11/2 inches have been developed and are well known to those skilled in the art. In nuclear applications, the combination of high operating temperature and pressure, potential hazard, and inaccessibility of parts to routine inspection and maintenance call for wall thickness well in excess of 11/2 inches, e.g. wall thickness as high as seven inches. Similarly, castings for sea water systems of deep diving submarines require thick Walls for withstanding high pressure and to compensate for corrosion.

Founding of completely sound thicker-walled castings,

3,446,236 Patented May 27, 1969 especially in alloys that solidify over a longer time, has proven to be exceptionally diiiicult. Percentage rejection has been very high. Even those deemed acceptable are not of as high quality as the more demanding service conditions require.

One of the defects has been shrinkage voids in the casting. Even when a thick-walled casting was founded with maximum risering, generally the risering was not adequate for proper directional solidication nor for preventing hot spots with the result that one or more shrinkage voids were left in the casting. Another of the defects has been microporosity due to slow solidiiication. To compound the problem, the chill layer which might provide added strength, uid tightness, and other desirable properties was generally removed by subsequent machining. The chill layer or chill skin of a casting is a layer of line-grain denser metal at the surface of a casting produced by the chilling action of the mold and core material. The thickness of the chill layer is dependent upon the pouring ternperature of the metal and the mass and thermal conductivity of the material against which the metal is poured. It is lwell known that this chill layer is stronger, denser and more leak resistant.

An object of this invention is to provide a method of producing sounder thicker-walled castings for fluid systems having generally superior properties.

A further object is to provide a method of producing higher quality, heavier wall thickness castings with a superior combination of corrosion resistance, strength-toweight ratio, weldability, pressure tightness, heat treatability, castability, impact strength and other desirable properties.

Other objects and advantages will appear from the following description of an example of the invention, and the novel features will be particularly pointed out in the appended claims.

FIG. l is a transverse section through a cylindrical casting founded in accordance with the teachings of this invention,

FIG. 2 is a longitudinal section through a valve body founded in accordance with the teachings of this invention, and

FIGS. 3 and 4 are perspective views of patterns for use in founding the casting shown in FIG. 2.

In its broader aspects this invention relates to a lamellar casting process wherein a thick-walled casting is founded in comparatively thin layers, each one fused to the preceding and succeeding layer, each layer formed by a separate pouring. Each pouring, after the first, adds some metal to the outside surface of the previously founded casting. Substantially the entire outer surface of each layer, except for the last layer, is cast with tapered thin-edged ridges or flutes so oriented as to be vertical when placed in the next mold for the succeeding pouring. Prior to each of the pourings, following the lirst, the previously founded casting is treated to attain a high-quality bond. At the very least, the surface of the previously founded casting is torched prior to the pouring to prevent condensation. For the successive layers of the same metal, e.g. steel on steel, and for many combinations of dissimilar metals, preheating of the previously founded casting is necessary. The preheating is carried out in place in the mold in the presence of an inert or reducing atmosphere to prevent oxidation or dross formation prior to the succeeding pouring. An induction coil around the mold, or a Calrod in the core, or electrical contacts in the core may be used for preheating. For some metals that do not bond well, the surface of the previously founded casting is coated with a mutually miscible metal e.g. tinning, or with a solution or suspension of one of various chemical fluxes known in the art, by means of dipping, spraying, or painting.

In FIG. 1 there is shown a transverse section of cylindrical pipe 10, fabricated in accordance with this invention and consisting of bonded cylindrical layers 12, 14, 16. The inner layer 12 is cast using conventional foundry technique in a sand mold having a vertical cavity formed with a pattern having the longitudinal sharp edged ridges 18 and terminated with core prints for locating the core in the mold.

A cylindrical sand core having a diameter that corresponds to the inside diameter of pipe and terminated with extra strong and hard core prints of the same configuration as the core prints on the pattern is mounted in the mold. Except for the extra strong and hard core prints on the core, the process is conventional. The layer 12 casting is removed from the mold with the core prints intact. The core prints are made extra strong and hard by inclusion of wire or mesh reinforcement and by adjusting the percentage of linseed oil. While protecting the core prints, the casting is grit based to remove all traces of the sand from the outer surface. A second mold is prepared using a pattern for the layer 14 but terminating with core prints identical to those on the previous pattern. The casting of the layer 12 with its core still in place is located in the second mold and is heated to a temperature below fusion but which will assure fusion of the first casting with the molten metal to be poured into the second mold. The casting may be heated with an induction coil formed around the mold flask; for this purpose the flask must be non-metallic. Alternatively the casting may be resistance heated by flowing current therethrough. For resistance heating electric contacts are molded into the sand core with surface area exposed to contact opposite end portions of the inside surface of the first casting 12 with the leads extending out of the core prints. Before the casting is heated, the mold is flushed and kept filled with inert gas, e.g. argon or a reducing gas. The procedure of grit blasting, molding, heating and pouring is repeated for founding the third layer on the second layer. The pattern for the outer layer is a circular cylinder to dene a smooth outer surface rather than grooves. The core is removed and the casting is complete.

Alternatively to using one sand core for founding the plurality of layers, a sand core with normal, rather than extra strong and hard, core prints may be used in founding the inner layer 12 and then removed and replaced with a metal core of approximately the same dimension and including a heating element therein such as a Calrod heating element for reheating the casting. Where the interior of the casting is not cylindrical the substituted metal core is in the form of end pieces corresponding to the core prints plus adjacent portions for seating in the casting; each of the substituted metal pieces includes a Calrod heating element. While the casting shown in FIG. 1 has three layers, the method may be practical to found a casting of two layers or four layers or more than four layers and is not limited to the cylindrical configuration described. The several layers may be of the same material or where advantageous they may be of different materials to impart desirable properties to the casting. For example if the casting is a valve body as in FIG. 2, the innermost layer 22 is preferably of a hard corrosion resistant alloy such as valve bronze for improved seat and interior surface life; the outermost layer 24 may be of an alloy which is comparatively easy to weld such as class B low-carbon steel; the intermediate layer 26 is preferably of pressure resistant alloy such as 70/30 cupro-nickel alloy.

For space applications a very light alloy such as magnesium-lithium alloy might be cast over a lining which has, for example, high corrosion resistance; in such cases it may be necessary to tin or metallize the lining before pouring the outer layer.

Patterns 28 and 30 for the inner and outer layers of the valve 20 are shown in FIGS. 3 and 4.

This invention includes the converse of the procedure described, namely starting with the largest dimension and adding consecutive smaller dimension inner layers.

In a lamellar casting there is a more substantial chill layer between each two consecutively founded metal layers than the chill layer formed against the sand mold or sand core. After the first pour, all subsequent pourings are made against a chill, the previous pour, which promotes a beneficial grain structure and reduces the tendency for shrinkage voids. The thickness of the chill layer is related to the pouring temperature of the latter founded layer and on the mass, temperature, and thermal conductivity of the previously founded layer.

To the extent that the engineer has been restricted heretofore to designing a casting around the properties of available materials, this invention enables the engineer to choose the best design and then select a material or materials with properties suitable to the design and with consideration to cost and servicing. For example, in castings for hard sea Water systems of deep-diving submarines, the casting must lhave high strength and corrosion resistance. Materials having the necessary corrosion resistance have low-strength compared to other materials; materials having the necessary strength have inadequate corrosion resistance. A lamellar casting in accordance with this invention can have an optimum combination of corrosion resistance and strength.

The photomicrograph in FIG. 5 illustrates the bonding achieved between layers. The photomicrograph is a 500x magnification of a nitric acid etch of the interface of a layer of steel 32 founded against a layer of copper-nickel alloy 30. Fragments of the steel alloy surface are diffused with copper-nickel and the copper-nickel penetrates into surface crevices 34 of the steel layer. Castings founded in accordance with this invention were tested by a number of techniques. One of the test techniques was the Dy-Chek method which employs a specific oil penetrant; bonds were found to be complete and sound. Radi- 'ography was used on 1x-inch slices of castings of coppernickel alloy and steel layers. The layers were found to be completely sound except for small particles of coppernickel torn off from the edges of the flutes or ridges and distributed through the steel layer. In order to test the strength of the Ibond, a 1s-inch-thick circular slice of a two layer casting of steel over a liner of copper-nickel alloy was subjected to a bulge test as follows. A ram, slightly smaller in diameter than the copper-nickel layer was forced down against the slice which was supported on a ring slightly larger in diameter than the copper-nickel layer. In effect, tensile stress was developed in the bond area due to the deformation of the plate. Failure occurred in the copper-nickel layer rather than at the bond demonstrating that the strength of the bond exceeded the strength of the copper-nickel layer.

Other advantages of lamellar casting techniques in accordance with this invention are as follows. The number and sizes of risers for each pouring are fewer and smaller than are required for a single pouring for the entire thick-Walled casting, thus reducing molding problems by reducing sand wall thickness and sand strengths required. For a lamellar casting, each pouring requires only a comparatively small heat which permits more acc-urate control of alloying, composition and temperatures. Following the founding of each layer of a lamellar casting, the casting may be examined by any of the various well known non-destructive testing methods; minor repairs may Ibe made to any layer before the next layer is poured. Chaplets may be utilized with impunity since their locations in founding the plurality of layers may be staggered in the various layers thus precluding the possibility of leakage due to a partially fused chaplet.

It will be understood that various changes in the details, materials and arrangements of parts (and steps), which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. A superior thick-walled valve housing of the type having -two end ports and an intermediate transverse port comprising a casting including a plurality of bonded together layers of dissimilar materials,

the interface between contiguous layers being formed by distributed intertting utes and grooves on the contiguous layers, each interface being a chill layer, the inner layer of the casting being a valve -bronze alloy for hardness, corrosion resistance, for providing superior seats and for longer interior surface life, -the inner layer including an integral wall portion between the end ports and having a portion transverse to the intermediate port and including an opening in-line with the intermediate port,

the outer layer of the casting being of class B low carbon steel for easy weldability,

and a layer of 70/ 30 cupro nickel alloy for pressure resistance between the inner and outer layers, the integral wall portion being free of other layers.

References Cited 5 UNITED STATES PATENTS Re. 17,362 7/ 1929 McWane 164-397 1,528,947 3/ 1925 Preston 164-105 3,165,983 l/1965 Thomas 164-397 925,809 6/1909 Henss 137-375 10 939,927 11/1909 Smith 251-366 1,697,083 1/ 1929 Phillips 251-368 XR FOREIGN PATENTS 15 105,075 10/ 1917 Great Britain. 1,044,271 6/ 1953 France.

SAMUEL SCOTT, Primary Examiner.

U.S. Cl. X.R. 20 251-368 

